a) 50 m
b) 72 m
c) 80 m
d) 82 m
Answer: a
Explanation:
$$\eqalign{
& {\text{Let the length of each train be }}x{\text{ metres}} \cr
& {\text{Then distance covered}} \cr
& {\text{ = 2x metres}} \cr
& {\text{Relative speed}} \cr
& {\text{ = (46}} – {\text{36)km/hr}} \cr
& {\text{ = }}\left( {10 \times \frac{5}{{18}}} \right)m/\sec \cr
& = \left( {\frac{{25}}{9}} \right)m/\sec \cr
& \frac{{2x}}{{36}} = \frac{{25}}{9} \Leftrightarrow 2x = 100 \Leftrightarrow x = 50 \cr} $$
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